It is known that one may increase the power delivered by an internal combustion engine by increasing the concentration of oxygen and fuel in the combustion, chambers. Systems employing this technique are widely used in the motor racing field. During normal operation, an internal combustion engine burns an air/fuel mixture consisting of vaporized fuel (supplied from a carburetor or fuel injectors) and air taken directly from the environment in which the engine is operating. It is known that one may increase the concentration of oxygen and fuel in the combustion chambers of an internal combustion engine by increasing the flow of fuel and displacing environmental air flowing into the engine from the air intake ports with an oxygen rich supply of air. One such widely practiced method for increasing the concentration of oxygen supplied to the engine is to deliver oxygen via disassociated nitrous oxide (N2O) to the air intake manifold of the engine.
It is currently neither practical nor advantageous to continuously deliver nitrous oxide whenever the engine is running. Therefore, one problem presented in the development of an effective nitrous oxide and fuel delivery system is determining how to engage the system at a point in time so that the accelerated combustion rate and increased energy supplied by the concentrated oxidizing agent/fuel mixture will enhance the power delivered by the engine without harming the engine or other components of the vehicle.
Typically, the driver enables the nitrous oxide supply system by closing a switch. The nitrous oxide delivery system may immediately administer nitrous oxide and additional fuel after the driver closes the switch, or alternatively the system may be placed in a ready state which must wait for the occurrence of at least one other condition precedent such as the passage of a predetermined period of time. One problem with the immediate administration of the nitrous oxide after an operator closes a switch is that the environment in which the nitrous oxide is utilized (high speed racing) does not favor the added distraction of having to flip a switch during mid-race conditions where the driver's attention is preferably focused upon directing the path of the vehicle and not to manipulating a switch to engage nitrous oxide when certain conditions have been observed by the driver. Therefore, it is desirable to have a control unit within the vehicle to automatically activate the nitrous oxide delivery system when certain relevant vehicle operating conditions have been sensed by the control unit.
A prior nitrous oxide delivery system delays the delivery of nitrous oxide a pre-set period of time after the driver depresses the accelerator. However, waiting a predetermined period of time before engaging the nitrous oxide system fails to account for additional relevant parameters which benefit drivers particularly interested in obtaining and maintaining maximum speed in order to travel a distance in the shortest period of time. It is, therefore, often desirable to utilize a nitrous oxide system that delivers nitrous oxide and additional fuel in response to the occurrence of conditions precedent, other than the passage of time, which are relevant to the optimal operation of the engine and vehicle.
Another problem associated with vehicles powered by nitrous oxide enhanced air/fuel mixtures is the sudden, considerable, increase in power delivered by an engine when the nitrous oxide delivery system is engaged and the concentrated air/fuel mixture begins to power the engine. The sudden increase in torque and horsepower may destabilized the vehicle and cause the driver to lose control of the vehicle. It is thus desirable for the nitrous delivery system, upon demand, to increase to full output at a rate which will provide the maximum power while maintaining the stability of the vehicle.
If additional fuel is not provided to the cylinders when nitrous oxide is added to the air entering the combustion chambers, the air/fuel mixture may "lean out" and as a result detonate instead of burning in a controlled manner. To prevent detonation and obtain maximum engine performance while nitrous oxide is delivered to the air/fuel mixture, additional fuel is added. Prior nitrous oxide systems provide sufficient additional fuel to the cylinders to maintain an air/fuel ratio which provides enhanced power output without detonation when the air/fuel mixture is ignited in the engine.
A proper air/fuel ratio must be maintained within each cylinder in order to obtain the full benefit of the enhanced concentration of oxidizing agent and fuel in the cylinders and to prevent harm to the engine. Prior systems have administered the additional fuel by means of a spray bar mounted at the air intake manifold. This method presents the problem of non-uniform dispersion of the added fuel to each of the cylinders. The additional fuel, small droplets delivered by the spray bar, lacks the mobility which would enable the fuel to disperse evenly in the distinct directions of the air intakes of the individual cylinders. Furthermore, the fuel may accumulate on the sides of the air intake runners before entering the cylinders. The result of these combined factors is that the ratio of the air/fuel mixture cannot be precisely controlled in each of the cylinders. Due to the poor dispersion qualities of the fuel droplets emitted from the spray bar, some cylinders may contain lean air/fuel mixtures while others may contain mixtures which are too rich. It is desirable to precisely control the rate at which fuel is added to each cylinder so that each cylinder burns an optimal ratio of fuel and air.
The fuel/air mixture is ignited in the combustion chamber shortly before the piston reaches the highest position in the cylinder (i.e. the combustion cavity is at its smallest). The period between the ignition and the point where the piston reaches its highest point is called the "spark advance". Spark advance enables the burning gases to exert an optimal force upon the piston resulting in a desirable transmission of energy from the burning air/fuel mixture to the drive shaft coupled to the pistons. Prior systems have adjusted the timing of the ignition as a function of engine speed in order to obtain a favorable conversion of heat energy produced by the burning air/fuel mixture into kinetic energy. However, these systems did not inject nitrous oxide and thus did not address the unique timing problems posed in nitrous oxide burning systems.
When a nitrous oxide delivery system increases the density of the oxidizing agent in the cylinders by injecting nitrous oxide into the flow of air entering the cylinders, the air/fuel mixture burns at an accelerated rate and consequently the maximum pressure in the cylinder is reached at a faster rate than when only environmental air is used to burn the fuel in the cylinders. If the ignition controller does not adjust the spark timing in order to compensate for this faster burn rate when nitrous oxide is added to the air/fuel mixture, the explosive force of the burning gases, even without detonation, will reach a maximum before the piston reaches its highest point in the cylinder. The gases will therefore exert a downward force upon the piston while the crank shaft continues to force the piston upward in the cylinder. Allowing these two forces to oppose one another in the manner described above not only decreases engine power output, it may also damage the engine and/or power train. In order to prevent the counter-productive and possibly destructive opposition of forces described above, the spark advance should be decreased (i.e. "retarded") a calibrated, pre-set, amount when nitrous oxide is added to the air/fuel mixture in order to prevent the explosive force of the burning air/fuel mixture from reaching a maximum until after the piston is on its downward path.
Another sign of too much spark advance is engine knock. This may occur due to a lean air/fuel mixture or erroneous advance calibration by the system designer. It is therefore desirable to provide a knock sensor and to provide a means for adjusting the spark advance in order to eliminate engine knock.
In general, nitrous oxide enhances the power delivered by an engine at a given engine speed. Though it is possible to build an engine and power train strong enough to withstand the increased force delivered by a nitrous oxide burning engine, many vehicles were not designed to endure the increased maximum horsepower and torque delivered by nitrous oxide systems. It is therefore desirable in many instances to adjust the spark advance in order to realize the enhanced output power of an engine at the extreme engine speeds of a given engine's power spectrum and bleed off some of the enhanced power potential at certain engine speeds where the output power and/or torque exceed the structural limitations of the engine or power train.
It is also desirable to provide means for allowing the user of the nitrous oxide system to easily tune the operation of the system by modifying the preprogrammed spark advance values. However, if such modification mechanisms are available to the user, additional safeguards should be included to protect the engine and vehicle against erroneous input values which may destroy the engine and/or drive train.
The ideal quantity of fuel added to a given volume of air changes when environmental conditions change. The ideal amount of fuel is affected by such factors as air temperature, barometric pressure, humidity, and impurities. It is thus desirable for the fuel delivery to modify the amount of fuel delivered to the cylinders in response to changes in environmental conditions. Some prior art fuel delivery systems measure factors such as those listed above directly and adjust the fuel delivery rate accordingly. An alternative system known in the prior art reacts to the level of oxygen in the engine exhaust and adjusts the fuel supply in order to obtain favorable levels of certain exhaust gases. More particularly, prior systems position oxygen sensors in the exhaust path which abruptly change state and provide a signal when the air/fuel ratio rises above or falls below a specific ratio. A common switch point in the prior systems was a 14.7 to 1 ratio. However, these oxygen sensing systems provide neither the necessary feedback for maintaining the desired air/fuel mixture for nitrous oxide combustion nor the appropriate information for determining the degree to which the air/fuel ratio deviates from the ideal ratio.